The H-bridge is a commonly known circuit which can be utilized as a driver to change the polarity of power delivered to a load using a unipolar power supply.
The operation of an exemplary H-bridge circuit will be discussed with respect to the circuit 100 of FIG. 1, which has been provided for reference only and is not intended to limit the scope of the disclosure. A typical H-bridge 110, includes a first switch SW1 connected between the power supply 120 and a first node 130, a second switch SW2 connected between the power supply 120 and a second node 140, a third switch SW3 connected between the first node 130 and ground 150, and a fourth switch SW4 connected between the second node 140 and ground 150. A load 160 is connected to the H-bridge between the first node 130 and the second node 140. A control circuit 170 manipulates the state of each of the switches so that at a given moment, only selected ones of the switches are closed (conductive). For example, if the first and fourth switches SW1, SW4 are closed and the second and third switches SW2, SW3 are open (non-conductive), the load 160 is powered with a polarity such that the potential at the first node 130, e.g. +V, is greater than the potential at the second node 140, e.g. ground. Conversely, opposite polarity at the load 160 (i.e. greater potential at the second node 140, e.g. +V, than at the first node 130, e.g. Ground) can be achieved by closing the second and third switches SW2, SW3 and opening the first and fourth switches SW1, SW4.
The control circuit 170 should operate such that switches along the same side of the H-bridge (i.e. first and third switches SW1, SW3, or second and fourth switches SW2, SW4) are not closed at the same moment. If this happens, a current could flow directly through both pairs of switches to ground without passing through the load 160. Such a situation is called “shoot-through current.” Shoot-through current is undesirable because it can cause excessive current through the switches, possibly destroying them, and overloading the power supply.
Existing control circuits aimed at preventing shoot-through current require the use of complicated digital logic. Others contain simpler shoot-through current prevention circuits, but require multiple input signals to operate. Some control circuits fail to properly prevent shoot-through current in the case that the control circuit is disconnected from feedback.